1. Field of the Invention
The invention relates to an alloy based on copper with zinc as an alloying constituent having the next to the highest share in the alloy.
2. Description of the Related Art
Such alloys, generally called brass, are used for the production of very different technical devices and components. Depending on the application, different alloying constituents are added to the brass alloys in order to obtain very specific properties which correspond to the respective intended use. If, for example, alloys are to be provided that are suitable for machining, the element lead is usually added to them in amounts of approximately 1 to 3 wt %. The lead has the effect that the chips occurring during machining are short-brittle. This characteristic is indispensable, particularly for the machining of workpieces on automatic machines.
When such lead-containing alloys are used for the production of components for the drinking water supply, there is the risk that the alloying constituent lead passes into the drinking water. Together with the drinking water, the lead reaches the human organism via the gastrointestinal tract, is mainly accumulated in the bones and leads to the known damage. Hazards due to lead are, however, also present in companies that produce lead-containing brass by melting or process products made from it. Here, the lead may enter the body through ingestion, inhalation or skin resorption.
It is known from DE 38 34 460 C2 to use an alloy for the production of components for water supply installations containing 1.5 to 7 wt % bismuth, 5 to 15 wt % zinc, 1 to 12 wt % tin and copper as remainder with accidental impurities. This is a red cast alloy which means a tin bronze with zinc as an additional alloying constituent. The disadvantage of such alloys is that they have a very wide solidification range because of the formation of a mixed substitution crystal between copper and zinc. This is a considerable disadvantage in that these alloys are only marginally suited for chill casting. This is mainly due to the fact that they have a relatively high melting temperature. The result of this is that, already after a few casting cycles, the chill molds become unusable owing to the high thermal stress. Furthermore, these alloys have a comparatively wide solidification range of approximately 150.degree. C. Together with the relatively high cooling rates in chill casting, this leads to an increased hot shortness of the cast parts. Therefore, the alloys mentioned above can virtually only be used for sand casting processes.
A further disadvantage of the known alloy is the fact that a relatively high bismuth portion is required to make machining possible.
On this basis, it is the object of the invention to provide an alloy that is low in lead content or that is lead-free and suitable for the production of components for drinking water installations, which does not have the above disadvantages. The alloy should continue to have the casting and mechanical properties necessary for the intended use. Water fittings, for example, should have a polishable surface and a pressure-tightness that is sufficient for the pressure ranges prevailing in drinking water supply systems, properties that depend directly on the fine-grainedness of the structure of the cast parts.